1. Field of the Invention
The present invention relates to a control device of an internal combustion engine, and particularly to a control device of an internal combustion engine, the control device controlling a power from the internal combustion engine coupled to an automatic transmission.
2. Description of the Background Art
Conventionally, a torque required for an engine has accurately been calculated to control the engine based on the calculated torque (target torque).
Japanese Patent Laying-Open No. 09-158772 discloses a control device of a diesel engine, the control device being capable of improving detection accuracy of an engine load. In the control device, an input shaft rotational speed (engine rotational speed) and an output shaft rotational speed (turbine rotational speed) of a torque converter coupled to the diesel engine are detected. Based on the detected input and output shafts rotational speeds of the torque converter, a velocity ratio is calculated. Based on the calculated velocity ratio, and by using a table showing a relation between the velocity ratio and the capacity coefficient of the torque converter, a capacity coefficient of the torque converter is calculated. Thereafter, based on the input shaft rotational speed (engine rotational speed) and the calculated capacity coefficient of the torque converter, an engine torque is calculated. The calculated engine torque is used as an engine load to control the diesel engine.
This control device focuses attention on the fact that an engine torque can be estimated by using a velocity ratio of the input and output shafts of the torque converter of the automatic transmission and a capacity coefficient specific to the torque converter. According to the control device, an engine load is accurately detected based on the detected input shaft rotational speed (engine rotational speed) and the detected output shaft rotational speed (turbine rotational speed) of the torque converter, which improves control accuracy in the diesel engine.
In a vehicle on which an automatic transmission with a torque converter is mounted, control has conventionally been provided to stabilize a power of an engine when the engine is in an idle state (an accelerator pedal is fully released) and when a drive range is selected in the automatic transmission (hereinafter this type of control is also referred to as “idle control”). In other words, the idle control is provided to stabilize the idle state of the engine when the vehicle is stopped (a drive range is selected) and when the vehicle creeps.
However, if the idle control above is provided to a vehicle having a gasoline engine mounted thereon, and the control method disclosed in the above-described Japanese Patent Laying-Open No. 09-158772 is applied, the following problem arises.
The control method disclosed in the Japanese Patent Laying-Open No. 09-158772 provides feedback control in which an engine load (engine torque) is controlled based on detected values of the input shaft rotational speed (engine rotational speed) and the output shaft rotational speed (turbine rotational speed) of the torque converter, resulting in control delay. Particularly if this control method is used to provide idle control in the gasoline engine, which has a generally slower torque response than a diesel engine, hunting may occur. Furthermore, the control method above requires integral control for controlling the engine load so that the engine load takes a target value during idle control. The integral operation is continually performed, resulting in enormous computational load.